1. Field of the Invention
The device pertains to magnetic disk drive motors applied to, e.g., floppy disk drive apparatuses or the like.
2. Related Art
Magnetic disk drive motors for driving to rotate media such as floppy disks are known. FIGS. 18 and 19 show an exemplary conventional magnetic disk drive motor. In FIG. 18, a housing 34 is cylindrical, and has two bearings 33, 33, upper and lower, fitted with the inner circumferential surface thereof. The bearings 33, 33 are made of a sintered member or the like. On the outer circumferential surface of the housing 34 is a collar portion 34a. On the bottom surface of the collar portion 34a is a stator core 35. The stator core 35 has a plurality of salient poles on the outer circumference thereof, and a coil 41 is wound around each salient pole. The thus constructed stator assembly with the housing 34 and the stator core 35 is mounted on a base plate 36. Between the base plate 36 and the bottom surface of the stator core 35 is a core holder 38, and a bottom portion of the core holder 38 is fitted into a hole 36a formed in the base plate 36.
A shaft 32 is inserted into the inner circumferential side of the bearings 33, 33 fitted with the inner circumferential surface of the housing 34. The shaft 32 not only is supported by the bearings 33 in the radial direction, but also has the bottom thereof supported by a thrust bearing 37 in the thrust direction. Thus, the shaft 32 is rotatable.
A hub stand 31 for carrying a medium or the like thereon is set and fixed to the top portion of the shaft 32, and a cuplike rotor case 40 is fixed to a lower edge portion of the hub stand 31 by caulking or the like. A drive magnet 42 is attached to the inner surface of the circumferential wall of the rotor case 40. The inner circumferential surface of the drive magnet 42 confronts the salient poles of the stator core 35 through a predetermined gap. As a result of this construction, the drive magnet 42 is energized by controlling electric conduction to the coil 41 wound around the salient poles, and the rotor 40 and the shaft 32 are therefore driven to rotate.
In the thus constructed conventional magnetic disk drive motor, the bearings 33, 33 are of the oil impregnated metal powdered type, and the shaft 32 is inserted into the bearings 33. As a result, there is a slight gap between the shaft 32 and the bearings 33, and this gap has been the source for causing vibration and play at the top of the shaft 32 when the magnetic disk drive motor is rotated.
The vibration and play caused at the top of the shaft 32 during the rotation of the magnetic disk drive motor is eliminated by applying lateral pressure to the shaft 32 and biasing a part of the outer circumferential surface of the shaft 32 onto the inner circumferential surface of the bearing 33. A lateral pressure applying method disclosed in Unexamined Japanese Utility Model Publication No. Hei. 2-88463 is such that a lateral pressure applying magnet is interposed between predetermined salient poles of the stator core and attracting a part of the rotor case with the lateral pressure applying magnet.
Progress in the downsizing or thin-sizing of floppy disk drive apparatuses and the like in recent years has led to a growing tendency toward the downsizing or thin-sizing of magnetic disk drive motors. However, when the magnetic disk drive motors are downsized, a sufficient space between the salient poles of the stator core 35 for mounting the lateral pressure applying magnet cannot be reserved. In addition, the thin-sizing of the magnetic disk drive motor leads to the thin-sizing of the lateral pressure applying magnet, which in turn reduces magnetically attracting force. Therefore, even if the lateral pressure applying magnet is used, it is difficult to obtain sufficient lateral pressure.
Further, to mount the lateral pressure applying magnet between the salient poles of the stator core 35 has been a factor for raising the assembling cost and the material cost.